Influence of Li₂O and Na₂O on Viscosity, Crystallization and Microstructure of High TiO₂-Containing Mold Slags

In the current study, the influence of Li2O and Na2O on the viscosity, crystallization, and structure of the high TiO2-containing mold slag for the continuous casting of high-Ti steel was investigated to improve the property of the CaO-SiO2-TiO2-based slag under the steel-slag reaction through the measurement of the viscosity-temperature relationship, crystallization temperature and phases, and the Raman spectrum. With the increase of Li2O content from 0 to 8 pct, the viscosity at 1300 degrees C and melting temperature decreased from 0.54 to 0.01 Pa s, and 1151 to 884 degrees C, respectively. While the viscosity of the slag at 1300 degrees C increased from 0.20 to 0.62 Pa s, the viscosity of the slag at 1400 degrees C decreased from 0.16 to 0.09 Pa s, and the melting temperature decreased from 1195 to 1077 degrees C with the Na2O content from 2 to 10 pct. According to the thermodynamic calculation and XRD measurement, the main crystallization phase of high TiO2 slags was CaTiO3 with the content of Li2O below 4 pct and Na2O of 2 to 10 pct, the crystallization phase gradually changed from CaTiO3 to LiTiO2 with Li2O from 4 to 8 pct, and the morphology of the crystalline nucleus changed from the type of spiky star to barbed sphere. Similarly, with the Li2O content from 2 to 6 pct the initial and complete crystallization temperature decreased and increased, respectively, while those increased with the increase of Na2O content, indicating that the increase of the Li2O below 4 pct and the decrease of the Na2O in the current slag resulted in the weak crystallization ability. With the addition of Li2O content, the complex structural units of Q(1), Q(2) and Q(3) were depolymerized, and the slag viscosity decreased. With the increase of Na2O content, structural units of Q(0), Q(1) and Q(2) structure units had the tendency to increase, and the viscosity of slag at 1400 degrees C decreased. These results could be used for the selection of typical components of mold slags for continuous casting of high-Ti steel.